The effect of organic acids on oxygen binding of hemocyanin from the crab Cancer magister

Abstract

1. 1. l-lactate raises the oxygen affinity of both stripped and unstripped hemocyanin (Hc) of Cancer magister. The effect of lactate is independent of pH in the range 6.8-8.3. 2. 2. d-lactate, glycolate and 2-methyl lactate also increase the Hc oxygen affinity, but to a lesser extent than l-lactate. Other structural analogues such as acetate, alanine, α-hydroxybutyrate, pyruvate and propionate have no effect on oxygen binding. 3. 3. These results suggest that C. magister Hc has an allosteric site with high specificity for L-lactate. 4. 4. The amount of lactate and H + in the blood of an exercised C. magister explains the change in Hc oxygen affinity brought about by high levels of locomotor activity. 5. 5. However, the amount of lactate in the blood of a resting crab does not explain the difference in Hc oxygen affinity between stripped and unstripped hemocyanin. 6. 6. End-products of anaerobic metabolism found in other taxa do not affect C. magister Hc oxygen binding. 7. 7. Thus, selection for an oxygen carrier with properties that respond to a particular form of anaerobic metabolism appears to have occurred. 8. 8. These findings confirm an earlier suggestion that an unidentified, low molecular weight factor is also present in crab hemolymph. 9. 9. The respiratory importance of the lactate effect following maximal locomotor activity is its enhancement of O 2 uptake at the gill rather than conservation of venous reserve at the tissues.